Monkman-Grant relation - analysis of first order kinetics of creep in AISI 304 stainless steel

The transient creep behaviour in AISI 304 Stainless Steel at 873 and 973 K for different test conditions obeyed first order kinetics and it was shown that the validity of Monkman-Grant relation (MGR) is a consequence of first order kinetics. The analysis is extended to tertiary creep regime and the results are found to obey first order kinetics for all test conditions. A new relationship between steady state and tertiary creep is proposed as epsilon over dot ((sic)(s))'.t(t)/epsilon(t) = constant (where t(t) and epsilon(t) are time spent in tertiary and the limiting tertiary creep strain respectively); alpha' is found to be unity for all test conditions implying the validity of first order kinetics. Further, this relation (for alpha' = 1) is found to be identical to modified Monkman - Grant relation (MMGR; m' = 1 where m' is the exponent for epsilon over dot (s) in MMGR) for the conditions satisfying f = 1/lambda and it is postulated that validity of MMGR is also a consequence of first order kinetics. When first order kinetics is applicable, a generalised relationship between steady state creep rate and rupture life is formulated and is valid for the results at all test conditions.